[CVE-2026-89458][MODERATE 7.0] s390/dasd: Do not complete a failed ESE read as successful

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-89458
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: s390/dasd: Do not complete a failed ESE read as successful
Commit: c9adf8399732306dfc97b3adb4778038743e3f5e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c9adf8399732306dfc97b3adb4778038743e3f5e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89458
Analysis date: Fri, 11 Sep 2026 17:17:14 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-89458 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89458

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: MODERATE 7.0
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-89458	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89458 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:L';CWE-908;*CWE-200;CWE-252;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:N';BEST CVSS score: '5.8';DESCR 'An s390 DASD ESE read of an unallocated track could be completed as successful even when ese_read failed before zeroing the destination buffer. In that case the block layer may receive stale or uninitialized memory instead of the expected zero filled data, which can expose sensitive data or return incorrect file or block contents. For the CVSS the PR:L is used because a local user or process with read access to the affected storage path may be enough to observe returned data, while administrative privileges are not necessarily required for every mounted filesystem case. The issue is not network reachable and depends on s390 DASD ESE thin provisioned devices plus a failed ESE read path, so AC:H is used. Impact is mainly confidentiality disclosure with limited integrity impact from incorrect read data, and possible limited availability impact in the paranoid score if stale data disrupts higher layer storage handling.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	YES	DANGER SIMPLEFIX ERRORPATH HARDWARE KPANIC 	NO	NO	checked

======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 5
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

No floor or cap changed the score.

2. Signal breakdown

Positive signals:

* +2: Direct stale or uninitialized memory exposure primitive. A failed ESE read can be completed as successful before the destination buffer is zeroed, so the block layer receives stale or uninitialized pages as valid read data.
* +1: Local below-host-admin read path. A local user or process with read access to the affected storage path may observe the returned data without needing host administrator privileges.
* +1: Important storage and block I/O path. The bug affects DASD block read completion semantics and can return incorrect contents to upper storage layers.
* +1: Concrete read-back consequence. This is not merely an internal invalid read. The request is completed successfully and stale data is handed upward as read data.

Negative or non-awarded signals:

* 0: No remote reachability. This is a local storage read path, not a network packet path.
* 0: No UAF or stale post-lifetime object use is established.
* 0: No arbitrary write, controlled reclaim, callback hijack, refcount takeover, or LPE primitive is established.
* 0: No crash or strong DoS point is awarded. The demonstrated consequence is incorrect successful completion and possible disclosure, not a kernel panic.
* 0: No race penalty. The supplied evidence describes an ordered error path, not a timing race.
* 0: No rare-hardware penalty applied. s390 DASD ESE is platform-specific, but the affected system class is exactly this storage environment, and conservative scoring should not assume the least exposed deployment.

3. Reachability analysis

The evaluated attacker is a local user or process that can cause reads from the affected DASD-backed storage path and observe returned data. The complete trigger depends on s390 DASD ESE thin-provisioned devices and an ESE read failure path where `ese_read()` returns before zeroing the destination buffer.

Host administrator privileges are not positively required for observing data returned through a readable mounted filesystem or otherwise readable storage path. Namespace-scoped privilege is not relevant here. No network reachability is established. No special race timing is required, but the vulnerable condition is constrained to the specific ESE read error cases described in the commit.

4. Primitive and severity interpretation

The exact primitive is successful completion of a failed ESE read with stale or uninitialized destination pages instead of zero-filled data. This is an information disclosure and data correctness issue in a storage read path, not a UAF, double release, OOB write, or active-object lifetime corruption.

PrimitiveClass is CLASS_A because the patch establishes a direct user-observable stale or uninitialized memory disclosure path through normal block read completion. The demonstrated consequence is confidentiality exposure and incorrect read contents. Privilege escalation is not demonstrated and should not be inferred.

ImportantCandidate is YES because user-visible uninitialized memory exposure from a kernel block driver requires manual security review even without a known LPE chain. AutoDowngradeAllowed is NO because automatically closing this as ordinary DoS or low-risk correctness would miss the concrete disclosure primitive.

5. One-sentence report phrase

A failed s390 DASD ESE read could be incorrectly completed as successful before the destination buffer was zeroed, allowing a local reader of the affected storage path to receive stale or uninitialized memory instead of zeros.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch establishes a concrete stale or uninitialized data exposure path through block read completion, and the sensitivity of the leaked contents depends on page and storage-layer context.

7. Call-site confidence

Call-site confidence: medium

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: s390/dasd: Do not complete a failed ESE read as successful
Commit: c9adf8399732306dfc97b3adb4778038743e3f5e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c9adf8399732306dfc97b3adb4778038743e3f5e

Commit description:

dasd_int_handler() completes an NRF read of an unallocated ESE track by
calling ese_read() and unconditionally marking the request
DASD_CQR_SUCCESS. dasd_eckd_ese_read() can return an error before it has
zeroed the destination buffer: a failed sense-data parse or a current
track outside the requested range both return early, leaving the
destination pages untouched. The request is still completed successfully,
so the block layer is handed stale / uninitialized memory instead of
zeros.

Check the ese_read() return value and fail the request through the normal
error path instead of forcing DASD_CQR_SUCCESS.

Fixes: 5e6bdd3 ("s390/dasd: fix data corruption for thin provisioned devices")
Cc: stable@vger.kernel.org
Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Link: https://patch.msgid.link/20260805111612.1285190-2-sth@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/s390/block/dasd.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c9adf8399732306dfc97b3adb4778038743e3f5e

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-89458 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89458

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:N
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:L
  The Best / paranoid CVSS score: 5.8

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: unknown
  Paranoid ActionableScore: 5

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).